Recently there has been considerable and increasing interest within the detergents industry in the production of detergent powders having a high bulk density, and these are tending to supersede the traditional porous spray-dried powders. High bulk density powders may be made either by post-tower densification of spray-dried powder, or by wholly non-tower routes involving dry-mixing, agglomeration, granulation and similar processes.
Detergent powders of high bulk density containing anionic surfactants may be prepared by processes involving the neutralisation of a liquid acid precursor of an anionic surfactant with a solid water-soluble alkaline inorganic material, for example, sodium carbonate. This step may be carried out in the presence of other ingredients of the desired final composition, for example, detergency builders: a so-called in-situ neutralisation process. Such a process may be carried out in a batch or continuous high-speed mixer/densifier, although subsequent process steps are generally required to arrive at the desired granular product. A number of such processes is disclosed in the art.
EP 420 317A (Unilever) discloses a process for the preparation of granular detergent compositions and components of high bulk density, which comprises reacting a liquid precursor of an anionic surfactant with a solid water-soluble alkaline inorganic material in a high-speed mixer/densifier, for example, a Lodige (Trade Mark) CB30 Recycler; treating the material in a moderate-speed densifier/granulator, for example, a Lodige Ploughshare (Trade Mark); and finally drying and/or cooling the material, for example, in a fluidised bed. In principle, the process may be used to prepare compositions containing5 to 60 wt % detergency builder, 5 to 25 wt % sodium carbonate, 5 to 40 wt % anionic surfactant, and optional soap and nonionic surfactant. The compositions exemplified contain 36 to 46 wt % builder (zeolite A), 13.3 to 16.6 wt % sodium carbonate, and 13.6 to 23.3 wt % anionic surfactant, plus various minor ingredients.
EP 506 184A (Unilever) discloses a single-step process for the continuous preparation of a granular detergent composition or component, wherein 20 to 45 wt % of a liquid acid precursor of an anionic surfactant (preferably primary alcohol sulphate) and at least an equivalent amount of a solid water-soluble alkaline inorganic material (preferably sodium carbonate) are continuously fed into a high-speed mixer/densifier, together with sufficient water for the neutralisation process. In this process the detergent material remains throughout the process in particulate or granular form, and no further processing steps are required to obtain material of the required particle size.
Other desired ingredients such as detergency builders may be fed in additional to the alkaline material. In principle the process may be used to prepare granular compositions containing 20 to 50 wt % builder, 5 to 70 wt % sodium carbonate, 20 to 45 wt % anionic surfactant, plus optional soap and nonionic surfactant. The compositions exemplified contain zeolite A builder (25 to 32 wt %), sodium carbonate (16 to 48 wt %), and primary alcohol sulphate (25 to 32 wt %). No example in which the builder is zeolite contains more than 32 wt % anionic surfactant, but other examples in which the builder is calcite plus carbonate contain anionic surfactant (alkylbenzene sulphonate in this case) at levels of 39.2 to 39.5 wt %, and it is stated that the calcite/carbonate builder system enables higher surfactant levels to be attained.
The prior art compositions all contain sodium carbonate, at levels of at least 13.3 wt %. The presence of sodium carbonate was considered essential in order to obtain a granule that has sufficiently low friability to be handled readily in the factory. The sodium carbonate is known to provide nucleation sites for crystallisation and hence to play an important part in powder structuring. However, its presence limits the amount of anionic surfactant that can be carried, and limits formulation freedom in that less space is available for other ingredients; high alkalinity may also be undesirable in products intended for washing delicate fabrics, or for washing by hand.
It has now been found that in a zeolite/sodium carbonate/anionic surfactant granule, the carbonate level may be lowered much further than was previously thought, especially when the anionic surfactant is primary alcohol sulphate (PAS), without the penalty of unacceptable friability, thus allowing extremely high anionic surfactant loadings to be achieved.
Particularly high anionic surfactant levels may be attained when the zeolite is zeolite P having a silicon to aluminium ratio not exceeding 1.33 (zeolite MAP) as disclosed in EP 384 070A (Unilever).
Granules based on zeolite MAP have been found also to have an additional advantage over similar granules based on conventional zeolite A in that they also disperse more readily and rapidly in water.
EP 521 635A (Unilever) relates to the use of zeolite MAP as a highly efficient carrier for liquid detergent ingredients, especially nonionic surfactants. The use of zeolite MAP to prepare high bulk density agglomerates is disclosed, containing in principle from 15 to 40 wt % of liquid active ingredient (for example, low-HLB nonionic surfactant), and an agglomerate containing 39 wt % nonionic surfactant is specifically disclosed.